1. Field of the Invention
The present invention relates to fabrics having salt-and-pepper patterns and, in particular, to denim warp yarns for producing these effects.
2. Description of the Prior Art
Fabrics having a "salt-and-pepper" pattern are desirable both for aesthetic reasons, such as fashion, as well as because such fabrics tend to obscure streaking and other dyeing variations. In order to produce this effect, the yarn has to be changed so it is capable of producing different shades of colors along it lengths after dyeing.
For filament yarns (i.e., polyester), this has been accomplished by one of three ways. One technique, illustrated in U.S. Pat. No. 3,177,644 issued to Aspy et al., includes using at least two different heat-settings or tow-drying temperatures to product different degrees of dyeing susceptibility in synthetic filament yarn. Thus, combining two or more different dye affinity types into a yarn will produce a fabric having the characteristic salt-and-pepper pattern. The second technique for filament yarns includes structurally transforming a single filament yarn along its length such that the filament yarn has different shades of color along its length on dyeing. A third method of making a fabric having salt-and-pepper pattern filament yarns is produced from a crimped filament yarn having S-twist and Z-twist portions distributed in alternation along the length of the filament yarn. When the fabric made from such crimped yarn is dyed, the tightly bound portions take a dark shade of color and the loosely bound portions a light shade, thereby producing a salt-and-pepper pattern. One such process is disclosed in U.S. Pat. No. 4,355,499 issued to Takai. The fabric produced by this process is actually an optical illusion since the individual fibers are equally dyed. Such techniques are not at all helpful in producing a salt-and-pepper look with denim fabric.
For natural fibers, such as cotton, the salt-and-pepper pattern can be created by first dyeing the yarn or fabric with a dye that normally dyes only the outer surface of the fiber bundle which gives the appearance of a ring when viewed in a cross-section of the fiber bundle, and subsequently abrading at least a portion of the dyed surface away either by chemical or physical means, such as "stone-washing". This method has not been completely satisfactory since considerable amount of the fabric must be abraded away before the salt-and-pepper pattern becomes apparent. It has, thus, become desirable to develop a cotton fabric having an improved salt-and-pepper pattern which at the same time will minimize the amount of yarn or fabric abrasion necessary to produce a satisfactory result.